Increased erythropoiesis in embryonic spleen of polycythemic mice. An indicator for erythropoietin production by the embryo.

The hemopoietic events in the embryonic mouse spleen were investigated in fetuses of polycythemic mothers. 12th and 13th day embryonic spleens showed a marked increase in the number of erythroid precursors at an advanced maturation stage, as compared to controls. In addition, an increased erythropoietic activity, measured by 59Fe incorporation into red blood cells of posthypoxic polycythemic mice, was found in the plasma of 12th and 13th day pregnant polycythemic mice, compared with controls, i.e. plasma of nonpregnant nonpolycythemic mice, of nonpregnant polycythemic mice, and of 12th and 13th day pregnant nonpolycythemic mice. Since polycythemic mice are presumed to have low erythropoietin level, the stimulation of erythropoiesis in the embryonic spleens of polycythemic mothers suggests that fetal erythropoiesis is independent of the maternal one. Moreover, the present results indicate that fetuses of polycythemic mothers not only produce their own erythropoietin, but are also able to increase markedly the maternal erythropoietin as a consequence of hypoxemic conditions.